In general, a spark plug that is used in an internal combustion engine comprises a center electrode that is fitted in a cylindrical metal shell via an insulator and a ground electrode having one end that is joined to the metal shell and the other end that faces a leading end of the center electrode. In addition, in order to improve the ignitability, a spark plug is also used which has a ground electrode having a noble metal tip that is convexly provided, while facing a leading end of a center electrode, to a ground electrode main body part extending to the leading end of the center electrode from a metal shell (for example, refer to Patent Document 1).
[Patent Document]
[Patent Document 1] Japanese Unexamined Patent Publication No. 2002-237365